The present invention is generally related to the field of data communications and, more particularly, is related to a system and method for selecting a data transmission mode in a data communications link between a client device and a server.
In data communications networks, it is often the case that a client device is in data communication with a server over various networks, etc. In one typical network arrangement, a client device may be linked to a server through both a local loop and a digital network. Specifically, such a client device may include a modem that is coupled to a line card in a central office through the local loop. The communication across the local loop is typically of an analog nature due to the limitations of the local loop as a data communications medium. The line card, in turn, is coupled to the digital network such as the Internet, etc. The line card thus provides access to the digital network for the client device. Using this network arrangement, a client device may communicate with a server or other device on the digital network. Essentially, an analog-to-digital transformation occurs in the line card for upstream data traffic and a digital-to-analog transformation occurs in the line card for downstream traffic.
In a given instance of communication between the client device and the server, a specific mode of data transmission may be established therebetween. The mode of data transmission may include nonlinear or linear pulse code modulation (PCM) depending upon the individual capabilities of the client device and the server. Generally, it is necessary that the line card support the particular mode of data transmission that is employed by the client device and the server. Unfortunately, cases can occur in which both the client device and the server support a particular mode of data transmission that is not supported by the line card. Consequently, the client device and the server are prevented from using the mode of data transmission not supported by the line card, resulting in data transmission that is less than optimum.
In light of the foregoing discussion, the present invention provides for a data communications network including respective systems and methods in a client, a line card or other conversion device, and a server to implement either a linear or a nonlinear PCM transmission mode for data communication.
According to the present invention, the client and the server negotiate with each other to establish a specific data communications mode. The data communications mode may be, for example, linear pulse code modulation (PCM) or nonlinear PCM. To begin, the client informs the server whether it supports nonlinear PCM, linear PCM, or both. In light of the client communications capability and the modes supported by the server itself, the server responds by informing the client which data communications mode is to be employed for further data communication. In the case that both the client and server support linear and nonlinear PCM, the server informs the client that linear PCM is to be used, such being more conducive to accurate high-speed data communication. In the case that one of either the client or the server only supports nonlinear mode, the server informs the client that nonlinear PCM is to be employed.
Assuming that linear PCM is specified as the data communications mode between the client and the server, the server then transmits a message to the line card that informs the line card that linear PCM is to be used. If the line card is capable of performing linear PCM, upon receiving the message from the server, the line card transitions to linear PCM to conduct the data exchange between the client and the server. If the line card does not support linear PCM, then it ignores the message from the server.
Any failure on the part of the line card to implement linear PCM as mandated by the server is discovered during subsequent startup negotiations between the client and the server. If such a failure is discovered, the client and the server revert back to nonlinear data communication accordingly. One advantage provided by the present invention is that clients and servers or other data communications devices may communicate with each other using an optimum data communications mode.
Other features and advantages of the present invention will become apparent to a person with ordinary skill in the art in view of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention.